UTRAN (Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network) is a collective term for base stations, often referred to as Node B's and radio network controllers (RNC) that are included in a UMTS radio access network. UMTS is a particular mobile radio access technology (RAT) common in Europe that uses wideband code division multiple access (W-CDMA) as an underlying standard. UTRAN can be used for circuit switched and packet switched traffic. In initial standards for supporting UMTS, the transport technology specified for an RNC/Node B interface was Asynchronous Transfer Mode (ATM).
RNCs provide control functionality for the Node B's. An RNC and a Node B can be co-located, but more often a single RNC is positioned to serve multiple Node B's. A Node B generally has minimum functionality, as it is controlled by a serving RNC.
A “logical” interface known as an “IuB” exists between the RNC and Node B. The UTRAN has three other logical interfaces for communicating with the rest of the UMTS radio access network. A first interface is an “Iu” interface for connecting the RNC to the core network. A second interface is a “Uu” interface for connecting the Node B to the mobile stations, for example cell phones or wireless modems in computers. A third interface is an “IuR” interface for connecting two RNCs.
FIG. 1 illustrates a portion of an example of a UMTS radio access network 100 using ATM as a transport technology in the IuB interface. A core network 115 is coupled to multiple RNCs; two are shown in the illustrated example, RNC 110 and RNC 112. The core network 115 is coupled to RNC 110 via logical interface Iu 116A and coupled to RNC 112 via logical interface Iu 116B. The two RNCs 110,112 are shown coupled together via logical interface IuR 113. RNC 110 is coupled to an operations and maintenance center (OMC) 120 over link 125. The OMC oversees the operation of the network. Each of the network elements includes operation and application management (OAM) functionality that is capable of interacting with the OMC. RNC 110 is coupled to an ATM network 130. Multiple Node B's, in the illustrated example three are shown 140A, 140B, 140C, are also coupled to the ATM network 130. Each RNC to Node B path represents a logical interface IuB between the two elements. The RNC 110 to Node B 140A connection is logical interface IuB 135A. The RNC 110 to Node B 140B connection is logical interface IuB 135B. The RNC 110 to Node B 140C connection is logical interface IuB 135C. Each Node B is in wireless communication with one or more mobile stations, more generally referred to as user equipment (UE). For example, Node B 140A is in communication with UE 141A and UE 141B, Node B 140B is in communication with UE 143A, UE 143B and UE 143C and Node B 140C is in communication with UE 145A and UE 145B. The Node B's and the UEs they serve are coupled via logical interfaces Uu. Node B 140A is in communication with UE 141A via Uu 142A and UE 141B via Uu 142B, Node B 140B is in communication with UE 143A via Uu 144A, UE 143B via Uu 143B and UE 143C via Uu 144C and Node B 140C is in communication with UE 145A via Uu 146A and UE 145B via Uu 146B.